Microwave gas discharge switching tubes

ABSTRACT

A microwave gas discharge switching tube is provided with a conductive wire grid mounted on the inside of its input window to shorten the recovery time following the termination of a heavily ionised gas discharge within the tube. The tube may additionally contain water vapour in known manner to further reduce the recovery time.

United States Patent [1 1 Broadhead Apr. 2, 1974 MICROWAVE GAS DISCHARGESWITCHING TUBES [75] Inventor: John Arthur Broadhead, Lincoln,

England [73] Assignee: English Electric Valve Company Limited,Chelmsford, Essex, England [22] Filed: Sept. 5, 1972 [2]] Appl. No.:286,349

[30] Foreign Application Priority Data Sept. 10, 1971 Great Britain42266/71 [52] US. Cl 315/39, 313/217, 333/13 [51] Int. Cl. I'IOIp 1/14[58] Field of Search 333/13; 313/217, 315/39 [56] References CitedUNITED STATES PATENTS 2,939,044 5/1960 Stanney et al. 333/13 PrimaryExaminerHerman Karl Saalbach Assistant Examiner-Darwin R. HostetterAttorney, Agent, or FirmBaldwin, Wight & Brown [5 7 1 ABSTRACT Amicrowave gas discharge switching tube is provided with a conductivewire grid mounted on the inside of its input window to shorten therecovery time following the termination of a heavily ionised gasdischarge within the tube. The tube may additionally contain watervapour in known manner to further reduce the recovery time.

11 Claims, 2 Drawing Figures MICROWAVE GAS DISCHARGE SWITCHING TUBES IThis invention relates to microwave gas discharge switching tubes.Microwave gas discharge switching tubes are used in waveguide systemsinvolving the transmission to an aerial of high energy microwave pulsesfrom a transmitter and the transmission of low energy signals receivedby the aerial to a receiver. The purpose of the gas discharge switchingtube, or duplexing tube, as it is commonly called, is to isolate thereceiver from the transmission system duringthe transmission of the highenergy microwave pulse from the transmitter. Examples of such tubes areTR tubes, ATR

tubes, pre-TR tubes and so forth. The required isolation is achieved bya heavily ionised gas discharge initiated and sustained by the highenergy microwave pulse from the transmitter, which gas discharge acts asan electrical shutter diverting the energy from one channel to theother. The speed with which the shutter" can be opened following a highenergy pulse from the transmitter is known as the recovery time and isdependent upon the speed with which the ionised gas discharge can bequenched.

For obvious reasons the recovery time is required to be as short aspossible.

One known method of quenching the discharge is to include in the gasfilling of the tubean agent with a high affinity for electrons. Usuallythis agent is water vapour. Whilst this results in an improved recoverytime the methodsuffers from the disadvantage that the satisfactory lifeof the tube is dependent upon the length of time that the requiredpartial pressure of the water vapour can be maintained, and it is foundin practice that the water vapour gradually disappears during operation.In addition, if the partial pressure of the water vapour is initiallyincreased to increase the satisfactory life of the tube the leakagethrough the tube also increases. Furthermore, whilst the water vapourquenches the discharge sufficiently rapidly for signals to be detectedat the receiver, ionisation tends to decay over a prolonged period and,in fact, persists for several microseconds. This prolonged decay of thelow density ionised gas gives rise to a continual change of phase in thetube which, for many applications, is unacceptable.

Many microwave discharge gas tubes include a primer or keep-aliveelectrode and in order to avoid the aforementioned difficulties it hasbeen suggested that the keep-alive electrode be located behind the inputwindow. Such an arrangement is, for example, described on page 73 etseq. of Microwave Gas Discharge Devices by A. Kraszewski, published byIliffe, 1967. Locating the keep-alive electrode behind the input window,however, involves a number of design and production difficulties andfurthermore, for broadband tubes the voltagewhich has been foundnecessary to achieve satisfactory recovery times is undesirably high.

The object of the present invention is to provide improved microwave gasdischarge switching tubes of satisfactory recovery time.

According to this invention, a microwave gas discharge switching tubeincludes a conductive structure connected across and in close proximityto the input window of said tube, said structure being so dimensionedand arranged as to present a negligible de-tuning admittance to amicrowave signal in operation.

Preferably said structure is in contact with said window.

Normally said structure is connected mechanically to a waveguide sectionforming the body of said tube. The structure may be electricallyconnected to the waveguide section or it may be electrically isolatedtherefrom. In this latter case the structure may be, of course, arrangedto have a voltage applied to it but this is not preferred.

Normally said window is mounted in the waveguide section by means of awindow frame in which case said structure may be connected across saidwindow frame. Said structure may consist of a wire or a grid or thecombination of a grid fixed to a wire, which wire is connected acrosssaid window, said grid usually extending perpendicularly to the plane ofsaid window.

Whilst the tube described above may be used on its own, as withthe knowntube it may be combined with a varactor limiter or any other solid statedevice. The

tube may also be of the primed or primerless type and with any of theknown combinations of internal and external tuning elements.

The invention is illustrated in and further described with reference tothe accompanying drawing in which,

FIG. 1 is a part cut away side elevation of a microwave gas dischargeswitching tube in accordance with the present invention and,

FIG. 2 is a section along the line AA of FIG. 1.

Referring to the drawing, in this case a TR tube for X-band frequenciesconsists of a section of wave-guide 1 having an input flange 2 and anoutput flange 3. Mounted in input flange 2' is an input window 4, whilstmounted in output flange 3 is an output window 5. The two windows aremounted in window frames 6 and 7 respectively. Tunable cones 9, togetherwith irises l0 constitute the tuning members for the tube. 11 is anexhaust tail by which the tube is evacuated. 12 is the primer orkeep-alive electrode cone assembly. The interior of the device includesa gas filling.

As so far described the device is as known per se.

In accordance with the present invention a conductive structure isconnected across the input window 4 of the tube. This conductivestructure consists of a wire 13 to which is secured a grid 14. The wire13 is mechanically connected to the window frame 6 in electrical contactat 15 and 16. The grid 14 extendsperpendicularly to the plane of theinput window 4 and is so dimensioned as to present a negligible detuningadmittance to the microwave signal handled by the tube in operation.

In operation the conductive structure consisting of wire 13 and grid 14acts to remove electrons from the decaying discharge during the recoveryperiod by a probing action. The effect of the structure is more markedat lower levels of ionisation. If, therefore, as is possible, the knownexpedient of introducing water vapour into the tube is also used, thestructure acts to reduce the otherwise prolonged time for decay of thelow density ionised gas towards the end of the recovery period, which aswas mentioned hereinbefore, is a characteristic of the use of watervapour alone. Thus the undesirable phase change which is a feature ofthe conventional tube using water vapour alone is reduced.

I claim:

1. In a microwave gas discharge switching tube including a body defininga wave guide section and having an input window; a conductive structureconnected across and in close proximity to said input window, saidstructure being so dimensioned and arranged as to present a negligiblede-tuning admittance to a microwave signal in operation.

2. A tube as claimed in claim 1 and wherein said structure is in contactwith said window.

3. A tube as claimed in claim 2 and wherein said structure is connectedmechanically to said body of said tube.

4. A tube as claimed in claim 3 and wherein said.

structure is electrically connected to said body.

5. A tube as claimed in claim 3 and wherein said structure iselectrically isolated from said body.

6. A tube as claimed in claim 3 and wherein said window is mounted insaid waveguide section by means of a window frame and said structure isconnected across said window frame.

7. A tube as claimed in claim 2 and wherein said structure consists of awire or a grid or a combination of a grid fixed to a wire, which wire isconnected across said window.

8. A microwave gas discharge switching tube comprising, in combination:

a body defining a waveguide section, an input closure at one end of thewaveguide section having an input window opening, an output closure atthe other end of the waveguide section having an output window openingand microwave transparent input and output wi'ndowsrespectively closingsaid input and output window openings whereby to define a hermiticallysealed cavity containing ionizable gas adapted to initiate and sustain aheavily ionized gas discharge in response to a high energy microwavesignal input through said input window; and

means for quenching said gas discharge rapidly upon termination of thehigh energy microwave signal and for suppressing prolonged decay of lowdensity ionized gas, said means including a conductive structure inclose proximity to said input window and extending across said windowessentially centrally thereof for effecting said suppression ofprolonged decay of low density ionized gas; said structure beingdimensional to present negligible detuning admittance to microwavesignal input.

9. A microwave gas discharge switching tube as defined in claim 8wherein said means also includes water vapor within said cavity foreffecting the rapid quenching of the gas discharge.

10. A microwave gas discharge switching tube as defined in claim 9wherein said conductive structure is a wire.

11. A microwave gas discharge switching tube as defined in claim 10wherein said conductive structure also includes a grid fixed to saidwire and extending therefrom in a plane normal to said input window.

1. In a microwave gas discharge switching tube including a body defininga wave guide section and having an input window; a conductive structureconnected across and in close proximity to said input window, saidstructure being so dimensioned and arranged as to present a negligiblede-tuning admittance to a microwave signal in operation.
 2. A tube asclaimed in claim 1 and wherein said structure is in contact with saidwindow.
 3. A tube as claimed in claim 2 and wherein said structure isconnected mechanically to said body of said tube.
 4. A tube as claimedin claim 3 and wherein said sTructure is electrically connected to saidbody.
 5. A tube as claimed in claim 3 and wherein said structure iselectrically isolated from said body.
 6. A tube as claimed in claim 3and wherein said window is mounted in said waveguide section by means ofa window frame and said structure is connected across said window frame.7. A tube as claimed in claim 2 and wherein said structure consists of awire or a grid or a combination of a grid fixed to a wire, which wire isconnected across said window.
 8. A microwave gas discharge switchingtube comprising, in combination: a body defining a waveguide section, aninput closure at one end of the waveguide section having an input windowopening, an output closure at the other end of the waveguide sectionhaving an output window opening and microwave transparent input andoutput windows respectively closing said input and output windowopenings whereby to define a hermitically sealed cavity containingionizable gas adapted to initiate and sustain a heavily ionized gasdischarge in response to a high energy microwave signal input throughsaid input window; and means for quenching said gas discharge rapidlyupon termination of the high energy microwave signal and for suppressingprolonged decay of low density ionized gas, said means including aconductive structure in close proximity to said input window andextending across said window essentially centrally thereof for effectingsaid suppression of prolonged decay of low density ionized gas; saidstructure being dimensional to present negligible de-tuning admittanceto microwave signal input.
 9. A microwave gas discharge switching tubeas defined in claim 8 wherein said means also includes water vaporwithin said cavity for effecting the rapid quenching of the gasdischarge.
 10. A microwave gas discharge switching tube as defined inclaim 9 wherein said conductive structure is a wire.
 11. A microwave gasdischarge switching tube as defined in claim 10 wherein said conductivestructure also includes a grid fixed to said wire and extendingtherefrom in a plane normal to said input window.